1. Field of the Invention
This invention relates to a method for recording or erasing information via a photo-recording medium (or an optical recording medium) having a recording film comprising a photochromic material as a main component.
2. Background Art
Photochromic materials have heretofore been used for filters for adjusting quantity of light, displays, actinometers, recording media for photographic printing, paints and so forth.
Furthermore, photochromic materials have recently attracted attention to the use as materials for photo-recording media in the field of photo-recording utilizing laser beams because of their possible utility for reversible memory media for high-density information recording.
Among methods for recording information via a photo-recording medium using a photochromic material for a recording film of the medium, there is known for example a method which comprises irradiating ultraviolet light beams of a specific wavelength onto the recording film in its non-colored state so as to convert the film into its colored state. In this method, it is known that when the recording film used has such a property that the peak of absorbance of the colored state appears in a visible region (i.e. not in an ultraviolet region) and the absorbance distribution of the colored state does not overlap with the absorbance distributions of the non-colored state in the vicinity of the peak of absorbance of the non-colored state which appears in an ultraviolet region, as shown in FIG. 5, it is best to use a wavelength of WL1 indicated in FIG. 5, i.e. a wavelength corresponding to the peak of the absorbance distribution of the non-colored state of the recording film, for the recording light to be irradiated onto the recording film.
On the other hand, there are known photochromic materials having such a property that, when used as materials for the recording film of a photo-recording medium, the absorbance distribution of the non-colored state of the film overlaps with the absorbance distribution of the colored state in the vicinity of the respective peaks of the both distributions, as shown in FIG. 1. When such photochromic materials are used for the recording film of a photo-recording medium, it is not always best to use a wavelength corresponding to the peak of absorbance distribution of the non-colored state of the recording film, for the recording light to be irradiated, since by the irradiation of the recording light having that wavelength a reaction toward the non-colored state may also proceed to some extent concurrently with a reaction toward the colored state in the recording film.
This also holds similarly in the adverse case where an erasing light is irradiated onto a recording film to convert it from its colored state into its non-colored state, thereby effecting erasure of information.
Accordingly, it is a primary object of this invention to provide a method for recording or erasing information via a photo-recording medium having a recording film comprising the above mentioned photochromic materials as a main component having such a property that the absorbance distributions of the colored and non-colored states thereof overlap in the vicinity of the respective peaks of the both distributions, wherein a light for recording and a light for erasing information are respectively used each having a best-selected wavelength.